Process of reducing aluminium from its fluoride salts by electrolysis



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- S c. HALL. PROCESS OF REDUGINGALUMINIUM FROM- ITS PLUOBIDE SALTS BY BLEGTBOLYSIS. No. 400,664. Patented Apr. 2, 1889.

" Falql To all whOm-it may concern:

UN TED STAT PATENT ()FFICE.

CHARLES M. HALL, or OBERLIN, onIo.

PROCESS OF REDUCING ALUMINIUM FROM ns nuomnr SALTS BY ELVECTROLYSIS.

1 v I SPECIFICATION forming part of. Letter Original application filed July 9, 1886, Serial No. 207,601.

Be it known that I, CHARLES M. IIALL, a citizen of the United States, residin g at Oberlin, in the county of Lorain; and State of Ohio, have invented certain new and useful .Im-

.provements in'the Process of Reducing Aluminium from its Fluoride Salts by Electrolysis; and I do hereby declare the following to be a full, clear, and exact description of the invent-ion, such as will enable others skilled in the art to which it appertains to make and use the same l a In an application, Serial No. 207,601, filed by .me J uly9, 1886,I havedescribed and claimed a process for reducing aluminium, consisting in dissolving alumina or the oxide of aluminium in a fused bath composed of the fluorides of aluminium and a metal more electro-positive than aluminium, and then passing an electric current through the fused mass, 'and in said application the combination ofthe fluorides of aluminium and sodium for the formation of the bath was claimed as a species or in Figs? and are views, partly in section, of

modified forms of crucible.

Inthe practice of my invention I form a;

fused bath or solvent for the alumina by melting in a crucible, A, a combination of the and the fluoride of potassium. This com bination, which may also be termed the double fluoride of aluminium and potassium, is preferably formed by mixing totions of the ingredients correspondingto the formula K Al F A variation in these pr portions-"with certain limitsproduces only salts known as the fluoride of aluminium Bream no. 400,664, dated. April 2, 1,889

Divided and this application filed February 2, 1887. Serial No. 226,206.

(No model.)

- immaterial changes in operativeness of my processas, for example, (as I now believe the fact to be,) a larger proportion of potassium fluoride increases the capacity of the bath for dissolving alumina at the sametime lessens its fusibility, Whereas a larger proportion of aluminium fluoride renders the bath more fusible, but decreases its capacity for dissolving alumina.

The combination of the fluorides of aluminium and potassium may be rendered morefusible and its capacity for dissolving alumina may be increased by the addition of lithium fluoride, or a partial substitution thereof,-

pounds or combinations of the fluorides of conveniently made by saturating and, neutralizing with hydrofluoric acid suitable proportions of hydrate of alumina and carbonate of potassium or lithium- The crucible A, containing the above-dcscribed bath or solvent, is placedjn a suitable furnace, B, and heated sufficiently 'to melt the bathi. 'e., to approximately a low red heat. The electrodes 0 and D, having suitable connections with a dynamo-electric machine or other suitable source of electric energy, are then inserted into the bath and a sufficient amount of aluminaplaced'. therein. The alumina is dissolved by the bath, and by the action, of the electric current aluminium is reduced at the negative electrode D, and, being melted, sinks down to the bottom of the crucible'. In making pure aluminium the negative electrode 'I) should be formed of carbon or metal coated with carbon, so as to protect the metal from the aluminiinn, which has a great. affinity: for other metals, The oxygen goes to the positive electrode (l, which may befonned of copper, platinum, or other suitable non-carbonaceous material. When the positive electrode is formed of copper, it soon becomes coated with an oxide of copper, which, wliile not materially affecting its oxygen, such oxygen thereafter escaping in a freestate at the positive electrode. The

- aluminium may be removed from the crucivble as it accumulates by any suitable means,

or the contents of the crucible may be poured out and cooled, and the aluminium thensepatated from the solvent.

On account of theaffinity which aluminium has for other metals, and also the corrosive action of fluorides on earthy materials, I prefer to form the crucible of metal-as iron, steel, copper, &c.and protect the same from theaction of aluminium by a carbon lining, A, as shown. The carbon lining A may be employed as the negative electrode, as shown in Figs. 2 and 3, and as it is desirable that the negative electrode should have a large exposed surface, I prefer an arrangement of apparatus wherein the carbon liningis so employed.

. Although a higher temperature may be employed, a low red heat is sufficient for carrying on the process, and on account of theliability of reducing the solvent I prefer to employ an electric current of low electro-motive force-as, for example, three or four volts, more or less.

As shown in Fig. 3, the crucible may be provided at its lower end with a discharge-tube, A through which the aluminium may be drawn off from the crucible from time to time, as desired, without interrupting the reducing operation.

I claim herein as my' invention 1. As an improvement in the art of manufacturing aluminium, the herein-described process, which consists in dissolving alumina in a-fused bath composed of the fluorides of aluminium and potassium, and then passing an electric current, by means of an anode formed of non-,carbon aceou s material, through the fused mass, substantially as set forth.

2. As an improvement in the art of manufacturing aluminium, the herein-described process, which consists in dissolving alumina in a fused bath composed of the fluorides of aluminium, potassium, and lithium, and then passing an electric current through the fused mass, substantially as set forth.

In testimony whereof Iaffix my sigi'iaturc in presence of two witnesses.

CHARLES M. HALL.

Witnesses:

M. A. BALLINGER, J. S. BRADFORD. 

